For the trade window issue, just click on the character portrait at the bottom left to have the appropriate person in the transaction.
As for the damage to Astarion, I noticed the same, and I think I figured it out.
The rule from 5e is actually live in where vampires are harmed by running water and take acid damage.
I was blown away when I figured it out because I couldn't believe it was implemented.
Astarion is fine in puddles and such, but crossing through lakes and streams or standing in open water areas like lakes or beaches will fry him.
